Path mechanisms such as MPLS (Multi-Protocol Label Switching), GMPLS (Generalized MPLS), MPLS-TP (MPLS Transfer Profile), and PBB-TE (Provider Backbone Bridge Traffic Engineering) have heretofore been proposed. In a network using such a path mechanism, link sharing in which plural backup paths may share the bandwidth of a link is proposed with the aim of efficient link bandwidth utilization (refer to IETF, “RSVP-TE Extensions For Shared-mesh Restoration in Transport Networks”, Internet-Drafts December 2001). In the link sharing, all backup paths are set up so that their bandwidths are guaranteed in case of faults occurring, if not exceeding a predetermined number of faults. This approach allows plural backup paths having different endpoints, respectively, to share the bandwidth of a link and, therefore, provides more efficient bandwidth utilization than path sharing in which plural active paths may share a backup path (refer to IETF, “Framework for Multi-Protocol Label Switching (MPLS)-based Recovery”, RFC 3469, February 2003).
Some techniques related to the link sharing have heretofore been disclosed, which are enumerated below: a method for advertising a shared bandwidth and a method for calculating a route (refer to JP-A No. 2003-273904); a method for setting up a high priority path preferentially in case of a fault occurring and a method for path setting by a centralized control server (refer to JP-A No. 2003-229889); and a path setting method taking wavelength into account (refer to JP-A No. 2005-210514).